ALK1ecd treatment in Bmp9-KO mice increases vascularization of the retina. (A-B) Visualization of blood vessels by isolectin B4 (iB4) staining of retinas at P5 from Bmp9-KO mice treated or not with ALK1ecd (5 mg/kg) injected at P1 and P3. (C) Bar graphs show the relative distance covered by the vascular plexus calculated as the ratio of the vascular radius over the retinal radius in percentage. (D-E) Higher magnifications of the retinas show that ALK1ecd treatment in Bmp9-KO mice lead to larger and multilayered blood vessels (see also z scan in panels F and G). Panels A through G show data from 2 litters containing 8 PBS treated Bmp9-KO mice and 7 ALK1ecd treated Bmp9-KO mice. Error bars show SEM. (A-B) Scale bar = 200 μm. (D-E) Scale bar = 25 μm.